Evaluation of the first immunoassay for the semi-quantitative measurement of meprobamate in human whole blood or plasma using biochip array technology Jean-Claude Alvarez a, ⁎, Charlotte Duverneuil a , Khémais Zouaoui a , Emuri Abe a , Philippe Charlier b , Geoffroy Lorin de la Grandmaison b , Stanislas Grassin-Delyle a a Laboratoire de Pharmacologie, Toxicologie, Centre Hospitalier Universitaire Raymond Poincaré, AP-HP, et Université Versailles Saint Quentin, 104 Boulevard Raymond Poincaré, 92380 Garches, France b Service d'Anatomie Pathologique et de Médecine Légale, Centre Hospitalier Universitaire Raymond Poincaré, AP-HP, et Université Versailles Saint Quentin, 104 Boulevard Raymond Poincaré, 92380 Garches, France abstract article info Article history: Received 19 September 2011 Received in revised form 19 October 2011 Accepted 19 October 2011 Available online 26 October 2011 Keywords: Meprobamate Carisoprodol Biochip array Human blood Immunoassay Background: Meprobamate is a carbamate, and the main metabolite of carisoprodol. It is used as an anxiolytic agent. Overdose of both drugs produces intoxication that is often serious and sometimes life threatening. However there was until now no immunoassay for the diagnosis of this intoxication. Methods: A chemiluminescent immunoassay for the semi-quantitative measurement of meprobamate in human blood and plasma has recently been developed, using the Evidence Investigator system (Randox®). In this study, the immunoassay was evaluated by testing drug-free (n = 10) or spiked whole blood and plasma samples (n = 70), and authentic post mortem whole blood samples from deceased patients in which meprobamate was present (n = 38) or not (n = 10). A previously validated gas chromatography– mass spectrometry (GC–MS) method was used for confirmation and quantification. 97 psychoactive drugs including carisoprodol were analyzed for possible interference. Results: With a cut-off at 0.5 mg/L, specificity, sensitivity and accuracy were 100%, 97.2% and 97.6%, respec- tively. All the untreated patients presented results under the cut-off. Meprobamate was not detected in three whole blood samples spiked with concentrations under the therapeutic range. In the authentic patients (n = 48), there were no false-negative results. A good correlation was found between the immunoassay and GC–MS (r = 0.90). Quantitative results of the immunoassay are approximately two-fold lower than GC–MS results. Only carisoprodol presented a cross-reactivity, 38 ± 6.6% at 10 mg/L, and 26 ± 4.8% at 100 mg/L. Conclusion: The first meprobamate immunoassay has shown very good specificity, selectivity and accuracy, which allow its use in hospital clinical laboratories for rapid diagnosis of meprobamate (or carisoprodol) intoxications. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Meprobamate belongs to the family of carbamates (Fig. 1), and is the main active metabolite of carisoprodol [1]. The first one is marketed as an anxiolytic agent and the second one as a centrally active muscle relaxant analgesic. These products induce depressant effects on the cen- tral nervous system (CNS) and have the potential to impair driving [2]. In the USA, they were in the 10 most frequently identified compounds in drug-impaired driving casework [3] and several case reports on the toxic potential of carisoprodol have been published [4,5]. Meprobamate has a barbiturate-like mode of action at the GABA A receptor and is able to induce the influx of chloride ions at high concentrations. In case of overdose, toxic effects include CNS depression, weakness, clonus, tachycardia, hypotension and respiratory depression. Death could occur resulting from hemodynamic disturbance and circulatory col- lapse, secondary to acute cardiac failure [6]. Meprobamate is involved in many suicide attempts and is implicated in 4 to 5% of the total deaths in France [7–9]. There is a good correlation between the blood concen- tration of meprobamate and its therapeutic or toxic effects [10]. Thera- peutic plasma concentrations are in the range 10–20 mg/L, and toxic effects appear at concentrations greater than 50 mg/L. A non-severe coma is classically observed with concentrations between 60 and 120 mg/L, while deep comas require concentrations above 120 mg/L. Death occurs with plasma concentration up to 200 mg/L. Considering this relationship, the 24/7 monitoring of meprobamate blood concen- tration is of great interest for the diagnosis of acute intoxications or even for the management of meprobamate elimination following hemodialysis. Several methods have already been reported for the quantification of meprobamate in human plasma or whole blood. Most of these methods are based on gas chromatography coupled with either flame ionization [11] or mass spectrometry detection Clinica Chimica Acta 413 (2012) 273–277 ⁎ Corresponding author at: Laboratoire de Pharmacologie, Toxicologie, Centre Hospi- talier Universitaire Raymond Poincaré, AP-HP, 104 Boulevard Raymond Poincaré, 92380 Garches, France. Tel.: +33 1 47 10 79 38; fax: +33 1 47 10 79 23. E-mail address: jean-claude.alvarez@rpc.aphp.fr (J.-C. Alvarez). 0009-8981/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cca.2011.10.025 Contents lists available at SciVerse ScienceDirect Clinica Chimica Acta journal homepage: www.elsevier.com/locate/clinchim